The long term of objective of this proposed work is to develop a practical monitoring system which nonivasively and continuously measures every significant parameter associated with the transport of oxygen and carbon dioxide. The system would have the additional features of required minimal patient contact and being noninterfering to gas exchange or any monitored parameters. Thus, the system would be available for monitoring applications ranging in disease serverity from critically ill patients to screening of normals. Monitoring would be applicable to patients ranging in size from newborn to adult and for activities ranging from sleep to exercise. The uniqueness of the methodology lies in 1) the use of the lung as a noninvasive port from which all significant gas exchange related information is available by analysis of tracer gas components, and 2) the simultaneous measurement and analysis of a sufficiently large and independent set of tracer components to provide characterization of all essential elements of the complex gas exchange process. The methodology has been developed under NIH sponsorship. The technologies required to support the methodology are 1) high powered computer technology with efficient software, and 2) mass spectroscopy which has a combination of sensitivity, frequency response, dynamic range, and accuracy, not yet found in practical instruments. The necessary computing power is now available at a practical cost. Also, because of recent advances in mass spectrometer technology, the development of a sufficiently low cost to support the development of a practical monitor appears feasible. However, firmly establishing such feasibility is a goal of Phase I of this proposal. The commercial development of the total monitor would be the goal for Phase II if Phase I is successful.